"Trough castable" is a term generally used to define refractory castable materials used in the iron-making industry. Trough castables are typically used in blast furnace cast house troughs and runners, tilting spouts, torpedo ladle cars, iron transfer ladles, iron mixers, cupolas and induction furnaces. In this wide range of applications, trough castables are exposed to many wear mechanisms that during normal operation will cause the refractory castable to corrode and erode away. Some of these wear mechanisms include thermal shock, iron erosion and slag corrosion.
Thermal shock relates to sudden and rapid changes in the temperature of a trough castable that may cause stresses to develop within the refractory material. These stresses can reduce the service life of the refractory lining through cracking and spalling. Iron erosion is caused by flowing molten metal mechanically eroding the exposed surface of the refractory castable. Molten iron may also attack the constituents such as silica and other oxides within the castable, and deteriorate the refractory properties of the material. Slag attacks the trough castable by forming lower temperature melting phases through various chemical reactions which makes the castable more susceptible to wear.
Basically, trough castables are designed to resist these different wear mechanisms through the use of specific types of raw materials in the formulation of the trough castable. In this respect, trough castables are typically comprised of alumina-silicon carbide-carbon (Al.sub.2 O.sub.3 --SiC--C). High alumina aggregate (such as fused alumina, sintered alumina or calcined bauxite) is the primary constituent in blast furnace trough castables. The high alumina aggregate has high density and low porosity to provide good resistance to metal and slag attack. The silicon carbide in the trough castable resists attack from slag, and helps protect the carbon within the trough castable from oxidizing. In addition, the silicon carbide acts as a volume stabilizer to minimize linear change when in service, and increases the thermal conductivity of the refractory material. The volume stability and higher conductivity characteristics of the silicon carbide help minimize damage from thermal shock. Carbon is added as a non-wetting compound to prevent adhesion of iron and slag to the castable. Carbon also increases the thermal conductivity of the castable.
In addition to the alumina, silicon carbide and carbon, trough castables include calcium aluminate cement. Low levels of calcium aluminate cement are used to minimize reaction between the calcium aluminate within the cement and slag. Fine aluminas and silicas are also typically added to trough castables to help promote good flow properties, corrosion resistance and hot strengths. Metals, such as silicon or aluminum, may also be added as antioxidants to protect the carbon, to aid in dry-out and to enhance the hot strength of the refractory material.
The present invention relates to an improved trough castable having increased resistance to furnace and cupolas slag through the use of fine magnesium aluminate spinel.